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Yosef Gruenbaum

Publications and source records attributed to Yosef Gruenbaum.

At least 19 recordsLinked to original sources
PubMed2006

Specific and conserved sequences in D. melanogaster and C. elegans lamins and histone H2A mediate the attachment of lamins to chromosomes.

The intimate association between nuclear lamins and chromatin is thought to regulate higher order chromatin organization. Previous studies have mapped a region between the rod domain and the Ig fold in the tail domain of Drosophila melanogaster lamin Dm0, which binds chromatin in vitro via the histone H2A/H2B dimer. This region contains an evolutionarily conserved nuclear localization signal (NLS) KRKR, and a sequence composed of the amino acids TRAT. Here we show that binding of lamin Dm0 to chromatin requires both NLS and TRAT sequences. Substituting either of the threonine residues in the TRAT sequence with negatively charged residues decreases the binding of lamin Dm0 to chromatin, indicating that this binding could be regulated by phosphorylation. Both lamin Dm0 and C. elegans Ce-lamin bind directly to histone H2A in vitro and this binding requires the NLS. The amino and carboxyl tail domains of histone H2A are each essential, but not sufficient, for binding to lamin Dm0; only a polypeptide containing both histone H2A tail domains binds efficiently to lamin Dm0. Taken together, these results suggest that specific residues in lamin Dm0 and histone H2A mediate the attachment of the nuclear lamina to chromosomes in vivo, which could have implications on the understanding of laminopathic diseases.

Amino Acid Sequence↗
PubMed2006

Matefin/SUN-1 is a nuclear envelope receptor for CED-4 during Caenorhabditis elegans apoptosis.

In Caenorhabditis elegans, the antiapoptotic protein CED-9 is localized at the mitochondria, where it binds the proapoptotic protein CED-4. Induction of apoptosis begins when the proapoptotic protein EGL-1 is expressed and binds CED-9. The binding of EGL-1 to CED-9 releases CED-4 from CED-9 and causes the activation of the caspase CED-3. Upon its release from CED-9, CED-4 rapidly translocates to the nuclear envelope (NE) in a CED-3-independent manner. However, the identity of the NE receptor for CED-4 and its possible role in the execution of apoptosis has remained unknown. Here, we show that the inner nuclear membrane SUN-domain protein matefin/SUN-1 is the NE receptor for CED-4. Our data demonstrate that matefin/SUN-1 binds CED-4 and is specifically required for CED-4 translocation and maintenance at the NE. The role of matefin/SUN-1 in the execution of apoptosis is further suggested by the significant reduction in the number of apoptotic cells in the organism after matefin/SUN-1 down-regulation by RNAi. The finding that matefin/SUN-1 is required for the execution of apoptosis adds an important link between cytoplasmic and nuclear apoptotic events.

Animals↗
PubMed2006

SUN-domain proteins: 'Velcro' that links the nucleoskeleton to the cytoskeleton.

The novel SUN-domain family of nuclear envelope proteins interacts with various KASH-domain partners to form SUN-domain-dependent 'bridges' across the inner and outer nuclear membranes. These bridges physically connect the nucleus to every major component of the cytoskeleton. SUN-domain proteins have diverse roles in nuclear positioning, centrosome localization, germ-cell development, telomere positioning and apoptosis. By serving both as mechanical adaptors and nuclear envelope receptors, we propose that SUN-domain proteins connect cytoplasmic and nucleoplasmic activities.

Animals↗
PubMed2006

The nuclear lamina and its proposed roles in tumorigenesis: projection on the hematologic malignancies and future targeted therapy.

The nuclear lamina, a network of lamin filaments and lamin-associated proteins, is located between the inner nuclear membrane and the peripheral chromatin. The nuclear lamina is involved in numerous nuclear functions including maintaining nuclear shape, determining nuclear positioning, organizing chromatin and regulating the cell cycle, DNA replication, transcription, cell differentiation, apoptosis, and aging. Alterations in the composition of nuclear lamins and their associated proteins are currently emerging as an additional event involved in malignant transformation, tumor propagation and progression, thus identifying potential novel targets for future anti-cancer therapy. Here, we review the current knowledge on lamin expression patterns in cells of hematologic malignancies and give an overview on the roles of the nuclear lamina proteins in heterochromatin organization, apoptosis, and aging with special emphasis on the relevance in cancer development.

Animals↗
PubMed2006

Solubility properties and specific assembly pathways of the B-type lamin from Caenorhabditis elegans.

Lamins are nucleus-specific intermediate filament (IF) proteins that together with a complex set of membrane proteins form a filamentous meshwork tightly adhering to the inner nuclear membrane and being associated with the nuclear pore complexes. This so-called nuclear lamina provides mechanical stability and, in addition, has been implicated in the spatial organization of the heterochromatin. While increasing knowledge on the biological function of lamins has been obtained in recent years, the assembly mechanism of lamin filaments at the molecular level has remained largely elusive. Therefore, we have now more systematically investigated lamin assembly in vitro. Using Caenorhabditis elegans lamin, which has been reported to assemble into 10-nm filaments under low ionic strength conditions, we investigated the assembly kinetics of this protein into filaments in more detail using both His-tagged and un-tagged recombinant proteins. In particular, we have characterized distinct intermediates in the filament assembly process by analytical ultracentrifugation, electron and atomic force microscopy. In contrast to the general view that lamins assemble only slowly into filaments, we show that in vitro association reactions are extremely fast, and depending on the ionic conditions employed, significant filamentous assemblies form within seconds.

Animals↗
PubMed2006

Nuclear lamins, diseases and aging.

Nuclear lamins are type V intermediate filament proteins. They are the major building blocks of the peripheral nuclear lamina, a complex meshwork of proteins underlying the inner nuclear membrane. In addition to providing nuclear shape and mechanical stability, they are required for chromatin organization, transcription regulation, DNA replication, nuclear assembly and nuclear positioning. Over the past few years, interest in the lamins has increased because of the identification of at least 12 distinct human diseases associated with mutations in the LMNA gene, which encodes A-type lamins. These diseases, collectively termed laminopathies, affect muscle, adipose, bone, nerve and skin cells and range from muscular dystrophies to accelerated aging.

Aging↗
PubMed2005

Age-related changes of nuclear architecture in Caenorhabditis elegans.

Mutations in lamins cause premature aging syndromes in humans, including the Hutchinson-Gilford Progeria Syndrome (HGPS) and Atypical Werner Syndrome. It has been shown that HGPS cells in culture undergo age-dependent progressive changes in nuclear architecture. However, it is unknown whether similar changes in nuclear architecture occur during the normal aging process. We have observed that major changes of nuclear architecture accompany Caenorhabditis elegans aging. We found that the nuclear architecture in most nonneuronal cell types undergoes progressive and stochastic age-dependent alterations, such as changes of nuclear shape and loss of peripheral heterochromatin. Furthermore, we show that the rate of these alterations is influenced by the insulin/IGF-1 like signaling pathway and that reducing the level of lamin and lamin-associated LEM domain proteins leads to shortening of lifespan. Our work not only provides evidence for changes of nuclear architecture during the normal aging process of a multicellular organism, but also suggests that HGPS is likely a result of acceleration of the normal aging process. Because the nucleus is vital for many cellular functions, our studies raise the possibility that the nucleus is a prominent focal point for regulating aging.

Aging↗
PubMed2005

Breaking and making of the nuclear envelope.

During mitosis, a single nucleus gives rise to two nuclei that are identical to the parent nucleus. Mitosis consists of a continuous sequence of events that must be carried out once and only once. Two such important events are the disassembly of the nuclear envelope (NE) during the first stages of mitosis, and its accurate reassembly during the last stages of mitosis. NE breakdown (NEBD) is initiated when maturation-promoting factor (MPF) enters the nucleus and starts phosphorylating nuclear pore complexes (NPCs) and nuclear lamina proteins, followed by NPC and lamina breakdown. Nuclear reassembly starts when nuclear membranes assemble onto the chromatin. This article focuses on the different models of NEBD and reassembly with emphasis on recent data.

Animals↗
PubMed2005

Barrier-to-autointegration factor is required to segregate and enclose chromosomes within the nuclear envelope and assemble the nuclear lamina.

Barrier-to-autointegration factor (BAF) binds dsDNA, LEM-domain proteins, and lamins. Caenorhabditis elegans BAF requires Ce-lamin and two LEM-domain proteins (Ce-emerin and Ce-MAN1) to localize during nuclear assembly. It was unknown whether Ce-lamin and LEM proteins, in turn, depend on Ce-BAF (mutually dependent structural roles). RNA interference-mediated down-regulation of Ce-BAF caused gross defects in chromosome segregation, chromatin decondensation, and mitotic progression as early as the two-cell stage, and embryos died at the approximately 100-cell stage. Nuclear pores reassembled, whereas Ce-lamin, Ce-emerin, and Ce-MAN1 bound chromatin but remained patchy and disorganized. The nuclear membranes formed but failed to enclose anaphase-bridged chromatin. Time-lapse imaging showed two phenotypes: anaphase-bridged chromatin that eventually resolved, and segregated chromatin that returned to the midzone. Thus, the assembly of BAF, lamins, and LEM-domain proteins is mutually dependent, and is required to capture segregated chromosomes within the nascent nuclear envelope. Embryos that escaped lethality by down-regulation of Ce-BAF grew into sterile adults with misplaced distal tip cells and gonads, further suggesting that mild postembryonic reductions in BAF disrupt tissue-specific functions.

Amino Acid Sequence↗
PubMed2005

The nuclear lamina comes of age.

Many nuclear proteins form lamin-dependent complexes, including LEM-domain proteins, nesprins and SUN-domain proteins. These complexes have roles in chromatin organization, gene regulation and signal transduction. Some link the nucleoskeleton to cytoskeletal structures, ensuring that the nucleus and centrosome assume appropriate intracellular positions. These complexes provide new insights into cell architecture, as well as a foundation for the understanding of the molecular mechanisms that underlie the human laminopathies - clinical disorders that range from Emery-Dreifuss muscular dystrophy to the accelerated ageing seen in Hutchinson-Gilford progeria syndrome.

Actins↗
PubMed2005

A lamin-dependent pathway that regulates nuclear organization, cell cycle progression and germ cell development.

The C. elegans genome encodes a single lamin protein (Ce-lamin), three LEM domain proteins (Ce-emerin, Ce-MAN1 and LEM-3) and a single BAF protein (Ce-BAF). Down-regulation of Ce-lamin causes embryonic lethality. Abnormalities include rapid changes in nuclear morphology during interphase, inability of cells to complete mitosis, abnormal condensation of chromatin, clustering of nuclear pore complexes (NPCs), and missing or abnormal germ cells. Ce-emerin and Ce-MAN1 are both embedded in the inner nuclear membrane, and both bind Ce-lamin and Ce-BAF; in addition, both require Ce-lamin for their localization. Mutations in human emerin cause X-linked recessive Emery-Dreifuss muscular dystrophy. In C. elegans, loss of Ce-emerin alone has no detectable phenotype, while loss of 90% Ce-MAN1 causes approximately 15% embryonic lethality. However in worms that lack Ce-emerin, a approximately 90% reduction of Ce-MAN1 is lethal to all embryos by the 100-cell stage, with a phenotype involving chromatin condensation and repeated cycles of anaphase chromosome bridging and cytokinesis. The anaphase-bridged chromatin retained a mitosis-specific phosphohistone H3 epitope, and failed to recruit detectable Ce-lamin or Ce-BAF. Down-regulation of Ce-BAF showed similar phenotypes. These findings suggest that lamin, LEM-domain proteins and BAF are part of a lamina network essential for chromatin organization and cell division, and that Ce-emerin and Ce-MAN1 share at least one and possibly multiple overlapping functions, which may be relevant to Emery-Dreifuss muscular dystrophy.

Animals↗
PubMed2004

Accumulation of mutant lamin A causes progressive changes in nuclear architecture in Hutchinson-Gilford progeria syndrome.

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder, commonly caused by a point mutation in the lamin A gene that results in a protein lacking 50 aa near the C terminus, denoted LADelta50. Here we show by light and electron microscopy that HGPS is associated with significant changes in nuclear shape, including lobulation of the nuclear envelope, thickening of the nuclear lamina, loss of peripheral heterochromatin, and clustering of nuclear pores. These structural defects worsen as HGPS cells age in culture, and their severity correlates with an apparent increase in LADelta50. Introduction of LADelta50 into normal cells by transfection or protein injection induces the same changes. We hypothesize that these alterations in nuclear structure are due to a concentration-dependent dominant-negative effect of LADelta50, leading to the disruption of lamin-related functions ranging from the maintenance of nuclear shape to regulation of gene expression and DNA replication.

Aged↗
PubMed2004

Matefin, a Caenorhabditis elegans germ line-specific SUN-domain nuclear membrane protein, is essential for early embryonic and germ cell development.

Caenorhabditis elegans mtf-1 encodes matefin, which has a predicted SUN domain, a coiled-coil region, an anti-erbB-2 IgG domain, and two hydrophobic regions. We show that matefin is a nuclear membrane protein that colocalizes in vivo with Ce-lamin, the single nuclear lamin protein in C. elegans, and binds Ce-lamin in vitro but does not require Ce-lamin for its localization. Matefin is detected in all embryonic cells until midembryogenesis and thereafter only in germ-line cells. Embryonic matefin is maternally deposited, and matefin is the first nuclear membrane protein known to have germ line-restricted expression. Animals homozygous for an mtf-1 deletion allele show that matefin is essential for germ line maturation and survival. However, matefin is also required for embryogenesis because mtf-1 (RNAi) embryos die around the approximately 300-cell stage with defects in nuclear structure, DNA content, and chromatin morphology. Down-regulating matefin in mes-3 animals only slightly enhances embryonic lethality, and elimination of UNC-84, the only other SUN-domain gene in C. elegans, has no affect on mtf-1 (RNAi) animals. Thus, mtf-1 mediates a previously uncharacterized pathway(s) required for embryogenesis as well as germ line proliferation or survival.

Animals↗
PubMed2003

Nuclear pore protein gp210 is essential for viability in HeLa cells and Caenorhabditis elegans.

Gp210 is an evolutionarily conserved membrane protein of the nuclear pore complex (NPC). We studied the phenotypes produced by RNAi-induced downregulation of gp210 in both human (HeLa) cells and Caenorhabditis elegans embryos. HeLa cell viability requires Gp210 activity. The dying cells accumulated clustered NPCs and aberrant membrane structures at the nuclear envelope, suggesting that gp210 is required directly or indirectly for nuclear pore formation and dilation as well as the anchoring or structural integrity of mature NPCs. Essential roles for gp210 were confirmed in C. elegans, where RNAi-induced reduction of gp210 caused embryonic lethality. The nuclear envelopes of embryos with reduced gp210 also had aberrant nuclear membrane structures and clustered NPCs, confirming that gp210 plays critical roles at the nuclear membrane through mechanisms that are conserved from nematodes to humans.

Animals↗
PubMed2003

Synchronization of interphase events depends neither on mitosis nor on cdk1.

Human HT2-19 cells with a conditional cdk1 mutation stop dividing upon cdk1 inactivation and undergo multiple rounds of endoreplication. We show herein that major cell cycle events remain synchronized in these endoreplicating cells. DNA replication alternates with gap phases and cell cycle-specific cyclin E expression is maintained. Centrosomes duplicate in synchrony with chromosome replication, giving rise to polyploid cells with multiple centrosomes. Centrosome migration, a typical prophase event, also takes place in endoreplicating cells. The timing of these events is unaffected by cdk1 inactivation compared with normally dividing cells. Nuclear lamina breakdown, in contrast, previously shown to be dependent on cdk1, does not take place in endoreplicating HT2-19 cells. Moreover, breakdown of all other major components of the nuclear lamina, like the inner nuclear membrane proteins and nuclear pore complexes, seems also to depend on cdk1. Interestingly, the APC/C ubiquitin ligase is activated in these endoreplicating cells by fzr but not by fzy. The oscillations of interphase events are thus independent of cdk1 and of mitosis but may depend on APC/Cfzr activity.

CDC2 Protein Kinase↗